Anion-jr interactions

Mascal [13] has also proposed the synthesis of three novel receptors for the binding of anions that take advantage of the high conformational stability of cylindrophane, which can effectively discriminate guests based on size. The receptors are designed to bind the anion through a combination of ion-pair reinforced hydrogen bonds and two anion-jr interactions. 

In the coordinated anionic polymerizations with Group I—III metal alkyls alone, monomer coordination involves overlap of the olefinic jr-electrons with vacant sp3 hybrid orbitals. Since this interaction is very weak it is most effective with easily polarized monomers. In the coordination polymerizations with Ziegler type catalysts, stronger monomer coordination is obtained by overlap of jr-electrons with vacant -orbitals of the transition metal component. The complexes have structures of the type proposed by Dewar (199b) and by Chatt and Duncanson (200) and applied to Ziegler type catalysts by Cossee (201) (Fig. 6). The olefin yr-electrons overlap with the orbital of... 

An alternative example of the metal-in-a-box model is provided by the monocationic [(Ph4B)Ba(thf)4][BPh4], shown in Figure 34. Here, the metal coordination sphere is completed by jr-arene interactions to a BPI14 anion, which binds in a sandwich-type interaction to the metal. Secondary, nonclassical interactions between the monocation and the noncoordinated anion provide additional stabilization. Interestingly, analogous reaction conditions for the smaller metals calcium and strontium afford the dicationic species [M(thf) ][BPli4]2 (M = Ca, n = 6 M = Sr, n = 7), that are... 

A systematic study of some monosubstituted solvent-separated cyclopentadienide salts of Group 1 cations (Li, Na, K, Cs) in DMSO revealed the bonding preferences for the fulvenoid (4) over the cyclopentadienyl isomer (5). Three of the substiments contained an a-carbonyl group formyl, acetyl and benzoyl. From the viewpoint of the anions, there is a conflict between the inherent greater stability of oxyanions over carbanions and the aromaticity associated with the 6 jr-electron carbocyclic system. The authors demonstrated that the fulvenoid interaction is favored by strong electron-accepting substituents and... 

In molecular orbital terms, the donation can be viewed as a HOMO-LUMO interaction (Chapter 9). Double hydrido bridges, as found in B H, also are exhibited by binieiallic species such as the chromium anion formed in Eq. 15.18. The similarity between these two dibridged species is underscored by the fact that their Lewis acid and Lewis base fragments can be interchanged (HCr(CO)jr reacts with BH, to form ... 

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